gem5  v21.1.0.2
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gem5::compression::FrequentValues Class Reference

This compressor samples the cache for a while, trying to define the most frequently used values. More...

#include <frequent_values.hh>

Inheritance diagram for gem5::compression::FrequentValues:
gem5::compression::Base gem5::SimObject gem5::EventManager gem5::Serializable gem5::Drainable gem5::statistics::Group gem5::Named

Classes

class  CompData
 
class  FrequentValuesListener
 
class  VFTEntry
 

Public Types

typedef FrequentValuesCompressorParams Params
 
- Public Types inherited from gem5::compression::Base
typedef BaseCacheCompressorParams Params
 
- Public Types inherited from gem5::SimObject
typedef SimObjectParams Params
 

Public Member Functions

 FrequentValues (const Params &p)
 
 ~FrequentValues ()=default
 
void probeNotify (const DataUpdate &data_update)
 Process a notification event from the ProbeListener. More...
 
void regProbeListeners () override
 Register probe listeners for this object. More...
 
- Public Member Functions inherited from gem5::compression::Base
 Base (const Params &p)
 
virtual ~Base ()=default
 
virtual void setCache (BaseCache *_cache)
 The cache can only be set once. More...
 
std::unique_ptr< CompressionDatacompress (const uint64_t *data, Cycles &comp_lat, Cycles &decomp_lat)
 Apply the compression process to the cache line. More...
 
Cycles getDecompressionLatency (const CacheBlk *blk)
 Get the decompression latency if the block is compressed. More...
 
- Public Member Functions inherited from gem5::SimObject
const Paramsparams () const
 
 SimObject (const Params &p)
 
virtual ~SimObject ()
 
virtual void init ()
 init() is called after all C++ SimObjects have been created and all ports are connected. More...
 
virtual void loadState (CheckpointIn &cp)
 loadState() is called on each SimObject when restoring from a checkpoint. More...
 
virtual void initState ()
 initState() is called on each SimObject when not restoring from a checkpoint. More...
 
virtual void regProbePoints ()
 Register probe points for this object. More...
 
ProbeManagergetProbeManager ()
 Get the probe manager for this object. More...
 
virtual PortgetPort (const std::string &if_name, PortID idx=InvalidPortID)
 Get a port with a given name and index. More...
 
virtual void startup ()
 startup() is the final initialization call before simulation. More...
 
DrainState drain () override
 Provide a default implementation of the drain interface for objects that don't need draining. More...
 
virtual void memWriteback ()
 Write back dirty buffers to memory using functional writes. More...
 
virtual void memInvalidate ()
 Invalidate the contents of memory buffers. More...
 
void serialize (CheckpointOut &cp) const override
 Serialize an object. More...
 
void unserialize (CheckpointIn &cp) override
 Unserialize an object. More...
 
- Public Member Functions inherited from gem5::EventManager
EventQueueeventQueue () const
 
void schedule (Event &event, Tick when)
 
void deschedule (Event &event)
 
void reschedule (Event &event, Tick when, bool always=false)
 
void schedule (Event *event, Tick when)
 
void deschedule (Event *event)
 
void reschedule (Event *event, Tick when, bool always=false)
 
void wakeupEventQueue (Tick when=(Tick) -1)
 This function is not needed by the usual gem5 event loop but may be necessary in derived EventQueues which host gem5 on other schedulers. More...
 
void setCurTick (Tick newVal)
 
 EventManager (EventManager &em)
 Event manger manages events in the event queue. More...
 
 EventManager (EventManager *em)
 
 EventManager (EventQueue *eq)
 
- Public Member Functions inherited from gem5::Serializable
 Serializable ()
 
virtual ~Serializable ()
 
void serializeSection (CheckpointOut &cp, const char *name) const
 Serialize an object into a new section. More...
 
void serializeSection (CheckpointOut &cp, const std::string &name) const
 
void unserializeSection (CheckpointIn &cp, const char *name)
 Unserialize an a child object. More...
 
void unserializeSection (CheckpointIn &cp, const std::string &name)
 
- Public Member Functions inherited from gem5::Drainable
DrainState drainState () const
 Return the current drain state of an object. More...
 
virtual void notifyFork ()
 Notify a child process of a fork. More...
 
- Public Member Functions inherited from gem5::statistics::Group
 Group (Group *parent, const char *name=nullptr)
 Construct a new statistics group. More...
 
virtual ~Group ()
 
virtual void regStats ()
 Callback to set stat parameters. More...
 
virtual void resetStats ()
 Callback to reset stats. More...
 
virtual void preDumpStats ()
 Callback before stats are dumped. More...
 
void addStat (statistics::Info *info)
 Register a stat with this group. More...
 
const std::map< std::string, Group * > & getStatGroups () const
 Get all child groups associated with this object. More...
 
const std::vector< Info * > & getStats () const
 Get all stats associated with this object. More...
 
void addStatGroup (const char *name, Group *block)
 Add a stat block as a child of this block. More...
 
const InforesolveStat (std::string name) const
 Resolve a stat by its name within this group. More...
 
void mergeStatGroup (Group *block)
 Merge the contents (stats & children) of a block to this block. More...
 
 Group ()=delete
 
 Group (const Group &)=delete
 
Groupoperator= (const Group &)=delete
 
- Public Member Functions inherited from gem5::Named
 Named (const std::string &name_)
 
virtual ~Named ()=default
 
virtual std::string name () const
 

Private Types

enum  Phase { SAMPLING, CODE_GENERATION, COMPRESSING }
 The phase that the compressor is at. More...
 
using DataUpdate = BaseCache::DataUpdate
 

Private Member Functions

void sampleValues (const std::vector< uint64_t > &data, bool is_invalidation)
 Sample values from a packet, adding them to the VFT. More...
 
void generateCodes ()
 End sampling phase and start the code generation. More...
 
std::unique_ptr< Base::CompressionDatacompress (const std::vector< Chunk > &chunks, Cycles &comp_lat, Cycles &decomp_lat) override
 Apply the compression process to the cache line. More...
 
void decompress (const CompressionData *comp_data, uint64_t *data) override
 Apply the decompression process to the compressed data. More...
 

Private Attributes

std::vector< FrequentValuesListener * > listeners
 
const bool useHuffmanEncoding
 Whether Huffman encoding is applied to the VFT indices. More...
 
encoder::Huffman indexEncoder
 The encoder applied to the VFT indices. More...
 
const int counterBits
 Number of bits in the saturating counters. More...
 
const Tick codeGenerationTicks
 Ticks needed to perform the CODE_GENERATION phase. More...
 
const bool checkSaturation
 Whether an action must be performed when counters saturate. More...
 
const unsigned numVFTEntries
 Maximum number of VFT entries, and thus of codewords too. More...
 
const unsigned numSamples
 Number of samples in the sampling phase. More...
 
unsigned takenSamples
 Number of samples taken so far. More...
 
Phase phase
 
AssociativeSet< VFTEntryVFT
 The Value Frequency Table, a small cache that keeps track and estimates the frequency distribution of values in the cache. More...
 
uint64_t uncompressedValue
 A pseudo value is used as the representation of uncompressed values. More...
 
EventFunctionWrapper codeGenerationEvent
 Event to handle finishing code generation and starting compression. More...
 

Additional Inherited Members

- Static Public Member Functions inherited from gem5::compression::Base
static void setDecompressionLatency (CacheBlk *blk, const Cycles lat)
 Set the decompression latency of compressed block. More...
 
static void setSizeBits (CacheBlk *blk, const std::size_t size_bits)
 Set the size of the compressed block, in bits. More...
 
- Static Public Member Functions inherited from gem5::SimObject
static void serializeAll (const std::string &cpt_dir)
 Create a checkpoint by serializing all SimObjects in the system. More...
 
static SimObjectfind (const char *name)
 Find the SimObject with the given name and return a pointer to it. More...
 
static void setSimObjectResolver (SimObjectResolver *resolver)
 There is a single object name resolver, and it is only set when simulation is restoring from checkpoints. More...
 
static SimObjectResolvergetSimObjectResolver ()
 There is a single object name resolver, and it is only set when simulation is restoring from checkpoints. More...
 
- Static Public Member Functions inherited from gem5::Serializable
static const std::string & currentSection ()
 Gets the fully-qualified name of the active section. More...
 
static void generateCheckpointOut (const std::string &cpt_dir, std::ofstream &outstream)
 Generate a checkpoint file so that the serialization can be routed to it. More...
 
- Protected Types inherited from gem5::compression::Base
typedef uint64_t Chunk
 A chunk is a basic lexical unit. More...
 
- Protected Member Functions inherited from gem5::compression::Base
std::vector< ChunktoChunks (const uint64_t *data) const
 This function splits the raw data into chunks, so that it can be parsed by the compressor. More...
 
void fromChunks (const std::vector< Chunk > &chunks, uint64_t *data) const
 This function re-joins the chunks to recreate the original data. More...
 
- Protected Member Functions inherited from gem5::Drainable
 Drainable ()
 
virtual ~Drainable ()
 
virtual void drainResume ()
 Resume execution after a successful drain. More...
 
void signalDrainDone () const
 Signal that an object is drained. More...
 
- Protected Attributes inherited from gem5::compression::Base
const std::size_t blkSize
 Uncompressed cache line size (in bytes). More...
 
const unsigned chunkSizeBits
 Chunk size, in number of bits. More...
 
const std::size_t sizeThreshold
 Size in bytes at which a compression is classified as bad and therefore the compressed block is restored to its uncompressed format. More...
 
const Cycles compChunksPerCycle
 Degree of parallelization of the compression process. More...
 
const Cycles compExtraLatency
 Extra latency added to compression due to packaging, shifting or other operations. More...
 
const Cycles decompChunksPerCycle
 Degree of parallelization of the decompression process. More...
 
const Cycles decompExtraLatency
 Extra latency added to decompression due to packaging, shifting or other operations. More...
 
BaseCachecache
 Pointer to the parent cache. More...
 
gem5::compression::Base::BaseStats stats
 
- Protected Attributes inherited from gem5::SimObject
const SimObjectParams & _params
 Cached copy of the object parameters. More...
 
- Protected Attributes inherited from gem5::EventManager
EventQueueeventq
 A pointer to this object's event queue. More...
 

Detailed Description

This compressor samples the cache for a while, trying to define the most frequently used values.

When these values are determined, they are associated to shorter representations (codes). Then the compressor can start its effective compression phase, in which occurrences of these values are substituted by their codes.

Definition at line 62 of file frequent_values.hh.

Member Typedef Documentation

◆ DataUpdate

Definition at line 67 of file frequent_values.hh.

◆ Params

typedef FrequentValuesCompressorParams gem5::compression::FrequentValues::Params

Definition at line 181 of file frequent_values.hh.

Member Enumeration Documentation

◆ Phase

The phase that the compressor is at.

It assumes that sampling and code generation are done only once.

Enumerator
SAMPLING 
CODE_GENERATION 
COMPRESSING 

Definition at line 112 of file frequent_values.hh.

Constructor & Destructor Documentation

◆ FrequentValues()

gem5::compression::FrequentValues::FrequentValues ( const Params p)

Definition at line 49 of file frequent_values.cc.

References COMPRESSING, and phase.

◆ ~FrequentValues()

gem5::compression::FrequentValues::~FrequentValues ( )
default

Member Function Documentation

◆ compress()

std::unique_ptr< Base::CompressionData > gem5::compression::FrequentValues::compress ( const std::vector< Chunk > &  chunks,
Cycles comp_lat,
Cycles decomp_lat 
)
overrideprivatevirtual

Apply the compression process to the cache line.

Returns the number of cycles used by the compressor, however it is usually covered by a good pipelined execution, and is currently ignored. The decompression latency is also returned, in order to avoid increasing simulation time and memory consumption.

Parameters
chunksThe cache line to be compressed, divided into chunks.
comp_latCompression latency in number of cycles.
decomp_latDecompression latency in number of cycles.
Returns
Cache line after compression.

Implements gem5::compression::Base.

Definition at line 64 of file frequent_values.cc.

References gem5::compression::Base::chunkSizeBits, gem5::compression::encoder::Code::code, gem5::compression::Base::compChunksPerCycle, gem5::compression::Base::compExtraLatency, COMPRESSING, gem5::compression::Base::decompChunksPerCycle, gem5::compression::Base::decompExtraLatency, DPRINTF, gem5::compression::encoder::Huffman::encode(), gem5::MipsISA::index, indexEncoder, gem5::compression::encoder::Code::length, numVFTEntries, phase, uncompressedValue, useHuffmanEncoding, and VFT.

◆ decompress()

void gem5::compression::FrequentValues::decompress ( const CompressionData comp_data,
uint64_t *  cache_line 
)
overrideprivatevirtual

Apply the decompression process to the compressed data.

Parameters
comp_dataCompressed cache line.
cache_lineThe cache line to be decompressed.

Implements gem5::compression::Base.

Definition at line 137 of file frequent_values.cc.

References gem5::compression::encoder::Code::code, gem5::compression::FrequentValues::CompData::compressedValues, COMPRESSING, data, DPRINTF, gem5::compression::encoder::Huffman::encode(), gem5::compression::Base::fromChunks(), indexEncoder, phase, uncompressedValue, useHuffmanEncoding, and VFT.

◆ generateCodes()

void gem5::compression::FrequentValues::generateCodes ( )
private

◆ probeNotify()

void gem5::compression::FrequentValues::probeNotify ( const DataUpdate data_update)

Process a notification event from the ProbeListener.

Parameters
data_updateThe data regarding the entry's contents update.

Definition at line 265 of file frequent_values.cc.

References generateCodes(), gem5::BaseCache::DataUpdate::newData, numSamples, gem5::BaseCache::DataUpdate::oldData, phase, sampleValues(), SAMPLING, and takenSamples.

Referenced by gem5::compression::FrequentValues::FrequentValuesListener::notify().

◆ regProbeListeners()

void gem5::compression::FrequentValues::regProbeListeners ( )
overridevirtual

Register probe listeners for this object.

No probe listeners by default, so do nothing in base.

Reimplemented from gem5::SimObject.

Definition at line 289 of file frequent_values.cc.

References gem5::compression::Base::cache, gem5::SimObject::getProbeManager(), and listeners.

◆ sampleValues()

void gem5::compression::FrequentValues::sampleValues ( const std::vector< uint64_t > &  data,
bool  is_invalidation 
)
private

Sample values from a packet, adding them to the VFT.

Parameters
dataThe line being sampled.
is_invalidationwhether this event comes from an invalidation.

Definition at line 177 of file frequent_values.cc.

References checkSaturation, gem5::compression::FrequentValues::VFTEntry::counter, data, gem5::GenericSatCounter< T >::isSaturated(), takenSamples, gem5::compression::Base::toChunks(), gem5::compression::FrequentValues::VFTEntry::value, and VFT.

Referenced by probeNotify().

Member Data Documentation

◆ checkSaturation

const bool gem5::compression::FrequentValues::checkSaturation
private

Whether an action must be performed when counters saturate.

Definition at line 97 of file frequent_values.hh.

Referenced by sampleValues().

◆ codeGenerationEvent

EventFunctionWrapper gem5::compression::FrequentValues::codeGenerationEvent
private

Event to handle finishing code generation and starting compression.

Definition at line 160 of file frequent_values.hh.

Referenced by generateCodes().

◆ codeGenerationTicks

const Tick gem5::compression::FrequentValues::codeGenerationTicks
private

Ticks needed to perform the CODE_GENERATION phase.

Definition at line 94 of file frequent_values.hh.

Referenced by generateCodes().

◆ counterBits

const int gem5::compression::FrequentValues::counterBits
private

Number of bits in the saturating counters.

Definition at line 91 of file frequent_values.hh.

◆ indexEncoder

encoder::Huffman gem5::compression::FrequentValues::indexEncoder
private

The encoder applied to the VFT indices.

Definition at line 88 of file frequent_values.hh.

Referenced by compress(), decompress(), and generateCodes().

◆ listeners

std::vector<FrequentValuesListener*> gem5::compression::FrequentValues::listeners
private

Definition at line 82 of file frequent_values.hh.

Referenced by regProbeListeners().

◆ numSamples

const unsigned gem5::compression::FrequentValues::numSamples
private

Number of samples in the sampling phase.

Definition at line 103 of file frequent_values.hh.

Referenced by probeNotify().

◆ numVFTEntries

const unsigned gem5::compression::FrequentValues::numVFTEntries
private

Maximum number of VFT entries, and thus of codewords too.

Definition at line 100 of file frequent_values.hh.

Referenced by compress(), and generateCodes().

◆ phase

Phase gem5::compression::FrequentValues::phase
private

Definition at line 113 of file frequent_values.hh.

Referenced by compress(), decompress(), FrequentValues(), generateCodes(), and probeNotify().

◆ takenSamples

unsigned gem5::compression::FrequentValues::takenSamples
private

Number of samples taken so far.

Definition at line 106 of file frequent_values.hh.

Referenced by probeNotify(), and sampleValues().

◆ uncompressedValue

uint64_t gem5::compression::FrequentValues::uncompressedValue
private

A pseudo value is used as the representation of uncompressed values.

This value is a random value that is not present in the VFT. It is selected at the end of the sampling phase.

Definition at line 157 of file frequent_values.hh.

Referenced by compress(), decompress(), and generateCodes().

◆ useHuffmanEncoding

const bool gem5::compression::FrequentValues::useHuffmanEncoding
private

Whether Huffman encoding is applied to the VFT indices.

Definition at line 85 of file frequent_values.hh.

Referenced by compress(), decompress(), and generateCodes().

◆ VFT

AssociativeSet<VFTEntry> gem5::compression::FrequentValues::VFT
private

The Value Frequency Table, a small cache that keeps track and estimates the frequency distribution of values in the cache.

Definition at line 150 of file frequent_values.hh.

Referenced by compress(), decompress(), generateCodes(), and sampleValues().


The documentation for this class was generated from the following files:

Generated on Tue Sep 21 2021 12:28:58 for gem5 by doxygen 1.8.17